Right. This is a list of the highest wicket takers at Sydney Cricket Ground.
http://stats.espncricinfo.com/australia/engine/records/bowling/most_wickets_career.html?class=1;id=132;type=ground
The list is comprised of 47 names - 19 of which are spinners which I'm sure is proportionally an awful lot higher than that of any other Australian test venue.
As you can see the most successful bowler of all time there is Shane Warne although I'm sure a lot of people will undo that statistic by saying that given the greatness of Warne it wouldn't need to be a spin friendly track for him to become the leader wicket taker.
So I'll focus on MacGill in the second spot. For this I'll compare him with Glenn McGrath, arguably one of the great seam bowlers in contemporary cricketing history, especially on Australian pitches.
McGrath played 12 tests at the SCG taking 50 wickets at a strike rate of 53.5 with a best of 5/48.
Meanwhile MacGill played 8 games, 4 less than McGrath, taking 53 wickets at a strike rate of 47.3 with a best of 7/50. All of those are firm, bold, factual
statistics so it's obvious MacGill has a better record than McGrath - given than MacGill wasn't as comparitevly as good a spin bowler as McGrath was a seamer you can only assume that it's due to the pitch being more condusive. Especially considering MacGill was barely ever a regular figure in the Australian side unless they were touring the sub-continent or when they were playing at
Sydney.
Now to dispell the comeback that given MacGill is a spinner he is likely to have bowler more overs, balls etc giving him an advantage.
In his 8 tests, MacGill bowled 2507 balls, while in his 12 tests McGrath bowled 2675 - 168 balls more than MacGill. Therefore while having an 168 ball advantage McGrath was still able to take 3 wickets less than MacGill.
Therefore I'll conclude that the only reason this is possible, given the abilities of the too comparatively compared in this paradigm you can only assume that MacGill took more wickets, in less time than McGrath not because he was a better bowler, but because he was a better bowler for the conditions available. AKA, the SCG spins, it has always spun, the next test shan't be any different, therefore it would much, much more statistical factual sense to play a spinner as they have a higher chance of succeeding.